[U-Boot] [linux-sunxi] Re: [PATCH 0/3] sunxi: sun8i-emac: Update DT bindings

Wed Jan 31 09:07:02 UTC 2018

Hi Maxime,

On Wed, Jan 31, 2018 at 7:36 PM, Maxime Ripard
<maxime.ripard at free-electrons.com> wrote:
> Hi Julian,
>
> On Wed, Jan 31, 2018 at 07:29:13PM +1100, Julian Calaby wrote:
>> Hi Maxime,
>>
>> On Wed, Jan 31, 2018 at 7:21 PM, Maxime Ripard
>> <maxime.ripard at free-electrons.com> wrote:
>> > Hi,
>> >
>> > On Mon, Jan 29, 2018 at 10:38:25AM +0000, Andre Przywara wrote:
>> >> On 29/01/18 09:58, Maxime Ripard wrote:
>> >> > On Mon, Jan 29, 2018 at 09:44:44AM +0000, Andre Przywara wrote:
>> >> >> On 29/01/18 08:51, Maxime Ripard wrote:
>> >> >>> On Mon, Jan 29, 2018 at 01:15:19AM +0000, Andre Przywara wrote:
>> >> >>>> The existing sun8i-emac driver in U-Boot uses some preliminary bindings,
>> >> >>>> which matched our own DTs. Now that the Linux kernel got a driver, lets
>> >> >>>> update our probe code to handle those Linux DTs as well.
>> >> >>>> The first patch adds the missing compatible strings for the pinctrl drivers,
>> >> >>>> which is needed for using the sunxi_name_to_gpio() lookup function.
>> >> >>>> Patch 2/3 updates the pinctrl parser used in the sun8i-emac driver, to cope
>> >> >>>> with the new, generic Allwinner pinctrl bindings.
>> >> >>>> The final patch extends the probe routine in the Ethernet driver to deal
>> >> >>>> with both the old and the new bindings.
>> >> >>>
>> >> >>> Thanks for posting this
>> >> >>>
>> >> >>>> This series allows to copy in the DTs from the latest kernel. Unfortunately
>> >> >>>> right now updating the DTs for the H5 and A64 breaks the build, as the
>> >> >>>> resulting binary (which embeds the DT) gets to large and triggers our new
>> >> >>>> image size check.
>> >> >>>
>> >> >>> Sigh...
>> >> >>>
>> >> >>>> As the H5 and H3 share most of the DT, we can't just update the H3
>> >> >>>> DTs either. Hopefully we find some neat trick to work around that.
>> >> >>>
>> >> >>> Is it just because of the DT size, or because there's more code?
>> >> >>
>> >> >> My impression the code itself is always growing a tiny bit over the
>> >> >> weeks, but this time around it's really the DT update.
>> >> >> The current A64 .dtbs in U-Boot are around 8KB, mainline is at 13KB.
>> >> >> Similar for the H5: going from 9.5KB to 14.5KB.
>> >> >>
>> >> >> Since you did a pretty good job already in identifying the code hogs, I
>> >> >> couldn't find *easy* mitigations over the weekend.
>> >> >> One possible fix is to remove the second .dtb in the Pine64 case, for
>> >> >> which I sent a patch Friday night.
>> >> >
>> >> > Since the DT is fed to the C preprocessor, we could also put some
>> >> > #ifdef 0 around the nodes that are never used by U-Boot (like the
>> >> > clocks, timer, psci, dma, GIC, RTC, RSB, etc.)
>> >>
>> >> Well yes, U-Boot itself actually only requires a *tiny* .dtb (I think
>> >> /aliases, /chosen, the reg of USB and Ethernet). But to be honest I
>> >> don't want to go there. First it would be a constant churn to keep this
>> >> up-to-date,
>> >
>> > I'm not too worried about the churn, it would be there only for the
>> > time until we fully migrate to the FAT environment, so one-two release
>> > now. And we're not syncing the DT very often these days (now that we
>> > have support for the EMAC and USB that is all U-Boot cares about).
>> >
>> >> but more importantly for proper UEFI boot we just reuse U-Boot's
>> >> .dtb to pass it on to the kernel. That is actually the purpose of
>> >> this whole exercise. That already works today (at least for A64),
>> >> but would benefit from some updates.
>> >>
>> >> So I would refrain from tinkering with U-Boot's .dtbs.
>> >
>> > That sucks :/
>> >
>> >> > This should give us some room.
>> >> >
>> >> >> Another thing that stuck out is the sha256 checksum. It's "default y" if
>> >> >> you have FIT. We need FIT for the SPL loader - but we don't do or need
>> >> >> the checksum there.
>> >> >> Some people do FIT loading for the kernel and initrd in U-Boot proper, I
>> >> >> suppose, but I am not sure how many depend on SHA256 checksums in their
>> >> >> images.
>> >> >
>> >> > I think there was someone (Tom?) that said that it was useful in some
>> >> > circumstances?
>> >>
>> >> Yes, I clearly see that it is *useful*, but I wonder how many people
>> >> would actually miss it today? We would bring it back once we dumped
>> >> ENV_IS_IN_MMC, so it's only temporarily.
>> >
>> > His words were stronger actually, and he said that we want to keep it.
>> >
>> >> I think we can just disable it in some defconfigs, to avoid collateral
>> >> damage to other boards.
>> >> If people have a special need, they can always disable the MMC env and
>> >> enable stuff at their likings, it's just the standard "make
>> >> .._defconfig; make" process that needs to be fixed with some band-aids
>> >> for now.
>> >
>> > I really don't want to go down the "let's fix each defconfig when we
>> > find out it broke", this is very likely to be broken with no-one
>> > noticing.
>> >
>> > Is this issue happening when you sync the whole DT, and would it break
>> > if you just convert the EMAC binding?
>> >
>> > Otherwise, we might try to revive the DTC garbage collection of unused
>> > nodes patches. This would prevent us from using the overlays on such a
>> > DT, but that doesn't like like an unfair tradeoff.
>>
>> Stupid question:
>
> It's not really stupid :)

Well it is, because I completely missed the UEFI case =)

>> As I understand it, the boot process is SPL => Full U-Boot => Linux.
>>
>> Would it therefore be possible to use a cut-down DT for the SPL (just
>> the bits it cares about) then use a full one afterwards?
>
> The thing is, we're not using the DT for the SPL, and the DT size
> we're discussing about is the one in the main U-Boot binary.
>
>> I'm guessing that the SPL wants to patch the DT we pass to Linux,
>> would we be able to handle that using overlays?
>
> In a "standard" setup (or at least the one you described), U-Boot will
> patch, or apply the overlay to, the DT provided by Linux, not its own,
> so even if we prevent the overlay usage on U-Boot's own, the only
> downside would be that the UEFI case Andre was describing would not
> work with overlays anymore.

So essentially I'm proposing a fix for a problem that doesn't exist.

I'll leave it at this.

Thanks for replying,

-- 
Julian Calaby

Email: julian.calaby at gmail.com
Profile: http://www.google.com/profiles/julian.calaby/